Gas-phase stereoselective binding to Mn/salen catalysts
Adelaide E Fagin1, Guoping Wang, Michel C Lau
1Department of Chemistry and Biochemistry, San Francisco State University, San Francisco, CA 94132, USA.
Organic Letters
|April 12, 2008
Summary
Gas-phase binding measurements reveal significant stereoselectivity for manganese/salen catalysts with 1-phenylethanol enantiomers. This gas-phase selectivity may predict condensed-phase enantioselectivity in asymmetric epoxidation.
Area of Science:
- Catalysis
- Stereochemistry
- Physical Organic Chemistry
Background:
- Asymmetric epoxidation is crucial for synthesizing chiral molecules.
- Understanding catalyst-substrate interactions is key to improving enantioselectivity.
- Gas-phase studies offer a unique perspective on binding events, free from solvent effects.
Purpose of the Study:
- To determine the gas-phase binding stereoselectivity of 1-phenylethanol enantiomers to manganese/salen catalysts.
- To compare gas-phase binding selectivity with condensed-phase epoxidation results.
- To validate a novel internal standard method for gas-phase binding measurements.
Main Methods:
- Gas-phase equilibrium measurements were employed.
- A novel internal standard approach was utilized for accurate quantification.
- Binding affinities of 1-phenylethanol enantiomers to manganese/salen catalysts were assessed.
Main Results:
- Significant stereoselectivity was observed in the gas-phase binding of enantiomers.
- The gas-phase binding stereoselectivity was compared with existing condensed-phase data.
- The novel internal standard method proved effective for rapid and accurate measurements.
Conclusions:
- Gas-phase binding stereoselectivity is a significant factor in asymmetric catalysis.
- Gas-phase binding stereoselectivity can potentially predict condensed-phase enantioselectivity.
- The developed method offers a valuable tool for studying gas-phase ligand-metal interactions.
Related Concept Videos
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
02:23SN2 Reaction: Stereochemistry
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
01:22Heterogeneous Catalysis
Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
02:26Preparation and Reactions of Sulfides
Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.